Method for preparing coal-based activated carbon through one-step activation of water vapor assisted by microwave heating

Abstract

The invention discloses a method for preparing coal-based activated carbon through one-step activation of water vapor assisted by microwave heating. Comprising the following steps: S1, raw material preparation: crushing low-rank coal to obtain a pulverized coal raw material; s2, adding an iron-based catalyst: mixing an iron-based catalyst solution with the pulverized coal raw material prepared in S1 to form a raw material to be mixed; s3, preparing a mixed material; s4, microwave activation; s5, acid pickling; s6, washing with water; and S7, drying. The method for preparing the coal-based activated carbon through one-step activation of water vapor assisted by microwave heating can be used for advanced treatment of industrial wastewater, purification of volatile organic compound waste gas, decoloration and refining of food and medicine products and recovery of precious metals. The method has the advantages that gasification reaction between carbon and an activating agent is accelerated, so that energy is saved, the activation efficiency is improved, the micropore and mesopore structure of activated carbon is favorably regulated, and functional groups on the surface of the activated carbon are regulated.

Description

Technical Field

[0001] This application relates to the fields of materials preparation and chemical technology, and more specifically, it relates to a method for preparing coal-based activated carbon by one-step microwave heating-assisted steam activation. Background Technology

[0002] Activated carbon is a porous carbon material prepared from coal through carbonization and physical or chemical activation processes. The core applications of activated carbon lie in its well-developed pore structure and huge specific surface area. It is mainly used as a highly efficient adsorbent for the purification of chemical raw material gases, catalyst carriers, solvent recovery, and deep purification of organic pollutants in wastewater. It is also used in the preparation of new chemical materials such as high-performance electrode materials and gas separation membranes. It is one of the key functional materials connecting the high-value utilization of coal resources with green chemical processes.

[0003] The activated carbon is activated by external heat conduction heating, but this method has the drawbacks of low thermal efficiency, slow heating rate and uneven heating, resulting in poor selectivity of activation reaction, irregular pore structure development and limited specific surface area, making it difficult to control the product performance. Summary of the Invention

[0004] To address the problem that activated carbon is activated by external heat conduction, resulting in irregular pore structure and limited specific surface area, this application provides a method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step.

[0005] This application provides a method for preparing coal-based activated carbon through one-step microwave heating-assisted steam activation, employing the following technical solution: A method for preparing coal-based activated carbon by one-step microwave heating-assisted steam activation includes the following steps: S1. Raw material preparation: Low-rank coal is crushed to obtain pulverized coal raw material; S2, Addition of iron-based catalyst: The iron-based catalyst solution is mixed with the coal powder raw material obtained in S1 to form the raw material to be mixed; S3. Preparation of Mixed Materials: The raw materials to be mixed obtained in S2 are mixed, and the optimal liquid-solid ratio, concentration, temperature and pH value are calculated and adjusted to obtain a uniform and fully impregnated mixture. The iron-based catalyst is uniformly dispersed in the coal powder to obtain a uniformly mixed powder. S4. Microwave activation: The mixed powder obtained in S3 is placed in a microwave field, and a mixture of water vapor and inert protective gas is introduced at the same time to activate it and obtain the activated material. S5. Pickling: The activated material obtained in S4 is soaked in acid to remove the iron element and obtain the pickled activated carbon intermediate. S6. Washing: The acid-washed activated carbon intermediate obtained in S5 is washed with deionized water until the washing solution is neutral and no chloride ions are detected, thus obtaining the water-washed activated carbon. S7. Drying: The activated carbon obtained in S6 after washing is dried to remove moisture and obtain coal-based activated carbon.

[0006] By adopting the above technical solution, and by using microwave heating and introducing an iron-based catalyst, the iron-based catalyst, as a powerful microwave absorber, can quickly convert microwave energy into heat energy during the activation process, achieving rapid and uniform heating of the material. At the same time, water vapor reacts with the coal char at high temperature to selectively etch the carbon skeleton to build well-developed pores, while the inert protective gas can inhibit the excessive oxidation and ablation of the raw materials. Therefore, this method can complete the activation process in one step with high efficiency, and obtain high-performance coal-based activated carbon with large specific surface area, rich pore structure, and well-developed micropores and mesopores.

[0007] Preferably, in step S1, the pretreatment of the coal powder raw material includes: crushing the raw coal to a particle size range of 40-200 mesh, and then oxidizing the crushed coal powder in air at 80-100°C for 3-7 days.

[0008] By adopting the above technical solution, the raw coal powder is controlled within the particle size range of 40-200 mesh, ensuring a certain mass and heat transfer efficiency during the subsequent mixing and activation process. The subsequent oxidation treatment in air at 80-100℃ for 3-7 days induces mild oxidation of the coal molecular structure, forming oxygen-containing functional groups. These functional groups not only provide active reaction sites for the subsequent steam activation stage, but also provide a surface chemical environment for the loading and dispersion of iron-based catalysts. Therefore, this pretreatment step improves the physical structure and surface chemical properties of the raw materials, providing a foundation for the high adsorption performance of the final activated carbon product.

[0009] Preferably, in step S2, the iron-based catalyst is ferric chloride hexahydrate prepared into an aqueous solution, with an iron salt FeCl3 concentration of 0.05–0.5 mol / L and 1 gram of carbon powder solution in 10–30 ml.

[0010] By adopting the above technical solution, ferric chloride hexahydrate is selected as the iron precursor because it can decompose into iron oxide or elemental iron nanoparticles with high microwave absorption efficiency during subsequent heat treatment. At the same time, the amount of iron-based catalyst added is controlled to 10ml to 30ml of carbon powder solution for every 1 gram of catalyst. Too low a loading is insufficient to produce a catalytic activation effect, while too high a loading will cause pore blockage and increase the burden on subsequent acid washing to remove iron. Therefore, this solution ensures that the iron-based catalyst can play its catalytic role efficiently during the activation stage, while ensuring the purity and pore structure quality of the final product.

[0011] Preferably, in step S3, the mixing treatment adopts the impregnation method, wherein the concentration of iron salt FeCl3 is 0.05-0.5 mol / L, 1 gram of carbon powder corresponds to 10 ml-30 ml of solution, the stirring temperature is 40℃-80℃, the pH value is 3.0-6.0, the stirring speed is 200 rpm-600 rpm, and the time is 30-120 min.

[0012] By adopting the above technical solution, the iron-based carbon powder is evenly dispersed. By calculating and adjusting the optimal liquid-solid ratio, concentration, temperature, and pH value, a uniformly and fully impregnated mixture is obtained. This ensures the uniformity of the subsequent activation reaction and also helps to partially disrupt the regular structure of the coal, increasing its reactivity. Therefore, this mixing process provides a guarantee for the rapid and uniform pore development in the subsequent microwave activation stage.

[0013] Preferably, in step S4, the microwave frequency of the microwave field is 2450MHz, the microwave power is controlled at 300-600W, and the activation time is controlled to be maintained at 30-100 minutes.

[0014] By adopting the above technical solution, the industrial standard 2450MHz microwave frequency is selected, the power is set between 300-600W, and the activation time is controlled between 30-100min. The appropriate combination of power and time avoids the collapse of the pore structure caused by local overheating, and also ensures that water vapor and carbon matrix have sufficient interaction time to form a pore structure.

[0015] Preferably, in step S4, the volume percentage of water vapor in the mixed gas is 30%-60%, and the inert protective gas is one or more of nitrogen, helium, or argon.

[0016] By adopting the above technical solution, limiting the volume fraction of water vapor in the mixed gas to 30%-60% is to control the intensity of the gasification reaction. If the proportion of water vapor is too low, the activation will be insufficient, and if it is too high, the carbon loss will be too great. At the same time, inert protective gases such as nitrogen, helium or argon are introduced to dilute the water vapor concentration and remove oxygen, preventing the material from burning at high temperature. They also provide a carrier channel for the gasification reaction products to be discharged. Therefore, this gas composition scheme ensures the efficient activation reaction while maintaining the safety and stability of the process.

[0017] Preferably, in step S5, the acid used is hydrochloric acid with a concentration of 1-2 mol / L, the soaking time is 1-5 hours, and the pickling temperature is maintained at 60-80℃.

[0018] By adopting the above technical solution, the activated material is soaked in a hydrochloric acid solution with a concentration of 1-2 mol / L at a temperature of 60-80℃ for 1-5 hours. This is based on the fact that iron species mainly exist in the form of metallic iron or iron oxide, and hydrochloric acid can react with them to form soluble iron salts for removal. At the same time, by controlling the appropriate temperature and time to ensure that the iron elements are fully leached out, unnecessary chemical corrosion of the already formed activated carbon skeleton is avoided. Therefore, this acid washing condition achieves a balance between efficient iron removal and protection of the carbon skeleton.

[0019] Preferably, in step S5, the liquid-solid mass ratio of the acid solution to the activated material is controlled to be (10:1) to (16:1).

[0020] By adopting the above technical solution, the liquid-solid mass ratio of acid solution to activated material is set within a certain range, thereby providing sufficient acid solution volume to ensure full contact between materials, while avoiding the use of excessive acid solution that would lead to an overload on subsequent wastewater treatment.

[0021] Preferably, in step S6, the washing is performed 2-4 times, with each wash using 3-5 times the mass of the activated carbon intermediate and each washing being agitated for 10-30 minutes; followed by soaking and washing in hot deionized water at 50-70°C for 30-60 minutes.

[0022] By adopting the above technical solution, the activated carbon product is washed in 2-4 steps, each time using 3-5 times the mass of deionized water compared to the activated carbon intermediate, accompanied by stirring for 10-30 minutes. This multi-displacement effect efficiently removes residual chloride ions and soluble salts. Subsequently, the product is soaked and washed in hot deionized water at 50-70℃ for 30-60 minutes. The increased temperature enhances the ion diffusion rate, ensuring thorough washing until the washing solution is neutral and free of chloride ions. Therefore, this washing process can guarantee the purity of the final activated carbon product and prevent impurities from affecting its application performance.

[0023] Preferably, in step S7, the drying temperature is controlled at 80-90°C until the quality of the activated carbon remains constant.

[0024] By adopting the above technical solution, moisture is removed slowly and thoroughly at a lower temperature, avoiding the decomposition of oxygen-containing functional groups on the surface of activated carbon or irreversible changes in the pore structure caused by excessively high temperatures, thereby maintaining its adsorption activity. Therefore, this drying condition can stabilize the product performance.

[0025] In summary, this application has the following beneficial effects: 1. This application introduces the synergistic effect of iron-based catalyst and microwave heating, enabling iron species to act as microwave absorbers during the activation stage, rapidly converting microwave energy into heat energy and achieving uniform heating of coal powder. Simultaneously, water vapor undergoes selective gasification reaction with the carbon matrix under high temperature, which can etch the carbon skeleton to build a porous structure, while the inert protective gas inhibits excessive oxidation and ablation of the carbon material, completing the activation and obtaining coal-based activated carbon with a high specific surface area structure of well-developed micropores and mesopores. This can improve the activation efficiency of activated carbon, regulate the pore structure and surface properties of activated carbon, and thus efficiently prepare high-performance coal-based activated carbon.

[0026] 2. This application controls the particle size of coal powder within a certain range and implements mild oxidation to induce the formation of oxygen-containing functional groups on the coal surface, providing an interfacial environment for subsequent steam activation and catalyst dispersion. At the same time, an impregnation method is used to allow iron-based materials to penetrate and disperse evenly into the carbon powder. By calculating and adjusting the optimal liquid-solid ratio, concentration, temperature, and pH value, a uniformly and fully impregnated mixture is obtained. Combined with the controlled microwave power and activation time, the activation reaction rate and pore development integrity can be balanced, further improving the adsorption performance and structural stability of activated carbon.

[0027] 3. This application improves the acid concentration, temperature and liquid-solid ratio to ensure that iron dissolves without damaging the pores, and removes residual ions and moisture through multi-stage water washing and gentle drying, ultimately ensuring the chemical purity and physical structural integrity of the activated carbon product, making it suitable for high-performance adsorption applications. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for preparing coal-based activated carbon by microwave heating-assisted steam activation proposed in this application. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0030] Example 1 This embodiment provides a method for preparing coal-based activated carbon through one-step microwave heating-assisted steam activation, comprising the following steps: S1. Raw material preparation: Low-rank coal is crushed to obtain pulverized coal raw material; The coal powder is crushed to 40 mesh and then oxidized in air at 80°C for 3 days.

[0031] S2, Addition of iron-based catalyst: The iron-based catalyst solution is mixed with the coal powder raw material obtained in S1 to form the raw material to be mixed; The iron-based catalyst is prepared as an aqueous solution of ferric chloride hexahydrate, with an iron salt FeCl3 concentration of 0.05 mol / L and 1 gram of carbon powder solution in 10 ml.

[0032] S3. Preparation of Mixed Materials: The raw materials to be mixed obtained in S2 are mixed, and the optimal liquid-solid ratio, concentration, temperature and pH value are calculated and adjusted to obtain a uniform and fully impregnated mixture. The mixing process employed an impregnation method, with an iron salt (FeCl3) concentration of 0.05 mol / L, 1 gram of carbon powder corresponding to 10 ml of solution, a stirring temperature of 40℃, a pH value of 3.0, a stirring speed of 200 rpm, and a stirring time of 30 minutes.

[0033] S4. Microwave activation: The mixed powder obtained in S3 is placed in a microwave field, and a mixture of water vapor and inert protective gas is introduced at the same time to activate it and obtain the activated material. The microwave frequency is 2450MHz, the microwave power is controlled at 300W, and the activation time is maintained at 30 minutes; the volume percentage of water vapor in the mixed gas is 30%, and the inert protective gas is nitrogen.

[0034] S5. Pickling: The activated material obtained in S4 is soaked in acid to remove the iron element and obtain the pickled activated carbon intermediate. The acid solution was hydrochloric acid with a concentration of 1 mol / L, the soaking time was 1 hour, and the pickling temperature was maintained at 60℃. The liquid-solid mass ratio of the acid solution to the activated material was 10:1.

[0035] S6. Washing: The acid-washed activated carbon intermediate obtained in S5 is washed with deionized water until the washing solution is neutral and no chloride ions are detected, thus obtaining the water-washed activated carbon. The process involves two washing cycles, each using three times the mass of the activated carbon intermediate, with each washing cycle consisting of 10 minutes of stirring. The carbon is then soaked in hot deionized water at 50°C for 30 minutes.

[0036] S7. Drying: The water-washed activated carbon obtained in S6 is dried to remove moisture and obtain coal-based activated carbon. The drying temperature is controlled at 80℃ until the quality of the activated carbon remains constant.

[0037] Example 2 This embodiment provides a method for preparing coal-based activated carbon through one-step microwave heating-assisted steam activation, comprising the following steps: S1. Raw material preparation: Low-rank coal is crushed to obtain pulverized coal raw material; The coal powder is crushed to 120 mesh and then oxidized in air at 90°C for 5 days.

[0038] S2, Addition of iron-based catalyst: The iron-based catalyst solution is mixed with the coal powder raw material obtained in S1 to form the raw material to be mixed; The iron-based catalyst is an aqueous solution of ferric chloride hexahydrate, with an iron salt FeCl3 concentration of 0.25 mol / L and 1 gram of carbon powder solution in 20 ml.

[0039] S3. Preparation of mixed materials: The raw materials to be mixed obtained in S2 are mixed to ensure that the iron-based catalyst is uniformly and fully impregnated. The mixing process employed an impregnation method, with an iron salt (FeCl3) concentration of 0.25 mol / L, 1 gram of carbon powder corresponding to 20 ml of solution, a stirring temperature of 60℃, a pH value of 4.5, a stirring speed of 400 rpm, and a stirring time of 75 min.

[0040] S4. Microwave activation: The mixture obtained in S3 is naturally dried and placed in a microwave field. At the same time, a mixture of water vapor and inert protective gas is introduced to activate the mixture and obtain the activated material. The microwave frequency is 2450MHz, the microwave power is controlled at 450W, and the activation time is maintained at 65 minutes; the volume percentage of water vapor in the mixed gas is 45%, and the inert protective gas is nitrogen.

[0041] S5. Pickling: The activated material obtained in S4 is soaked in acid to remove the iron element and obtain the pickled activated carbon intermediate. The acid solution was hydrochloric acid with a concentration of 1.5 mol / L, the soaking time was 3 hours, and the pickling temperature was maintained at 70℃; the liquid-solid mass ratio of the acid solution to the activated material was 13:1.

[0042] S6. Washing: The acid-washed activated carbon intermediate obtained in S5 is washed with deionized water until the washing solution is neutral and no chloride ions are detected, thus obtaining the water-washed activated carbon. The process involves washing three times, with each wash using four times the mass of the activated carbon intermediate, and each wash lasting 20 minutes with stirring. The carbon is then soaked in hot deionized water at 60°C for 45 minutes.

[0043] S7. Drying: The water-washed activated carbon obtained in S6 is dried to remove moisture and obtain coal-based activated carbon. The drying temperature is controlled at 85℃ until the quality of the activated carbon remains constant.

[0044] Example 3 This embodiment provides a method for preparing coal-based activated carbon through one-step microwave heating-assisted steam activation, comprising the following steps: S1. Raw material preparation: Low-rank coal is crushed to obtain pulverized coal raw material; The coal powder is crushed to 200 mesh and then oxidized in air at 100°C for 7 days.

[0045] S2, Addition of iron-based catalyst: Add the iron-based catalyst solution to the pulverized coal raw material obtained in S1 to form the raw material to be mixed; The iron-based catalyst is an aqueous solution of ferric chloride hexahydrate, with an iron salt FeCl3 concentration of 0.5 mol / L and a carbon powder solution of 1 gram in 30 ml.

[0046] S3. Preparation of Mixed Materials: The raw materials to be mixed obtained in S2 are mixed, and the optimal liquid-solid ratio, concentration, temperature and pH value are calculated and adjusted to obtain a uniformly and fully impregnated mixture.

[0047] The mixing treatment adopted the impregnation method, with an iron salt FeCl3 concentration of 0.5 mol / L, 1 gram of carbon powder solution in 30 ml, stirring temperature of 80℃, pH value of 6.0, stirring speed of 600 rpm, and time of 120 min.

[0048] S4. Microwave activation: The mixture obtained in S3 is naturally dried and placed in a microwave field. At the same time, a mixture of water vapor and inert protective gas is introduced to activate the mixture and obtain the activated material. The microwave frequency is 2450MHz, the microwave power is controlled at 600W, and the activation time is maintained at 100 minutes; the volume percentage of water vapor in the mixed gas is 60%, and the inert protective gas is nitrogen.

[0049] S5. Pickling: The activated material obtained in S4 is soaked in acid to remove the iron element and obtain the pickled activated carbon intermediate. The acid solution was hydrochloric acid with a concentration of 2 mol / L, the soaking time was 5 hours, and the pickling temperature was maintained at 80℃; the liquid-solid mass ratio of the acid solution to the activated material was 16:1.

[0050] S6. Washing: The acid-washed activated carbon intermediate obtained in S5 is washed with deionized water until the washing solution is neutral and no chloride ions are detected, thus obtaining the water-washed activated carbon. The process involves washing four times, with each wash using five times the mass of the activated carbon intermediate, and each wash lasting 30 minutes with stirring. The carbon is then soaked in hot deionized water at 70°C for 60 minutes.

[0051] S7. Drying: The water-washed activated carbon obtained in S6 is dried to remove moisture and obtain coal-based activated carbon. The drying temperature is controlled at 90℃ until the quality of the activated carbon remains constant.

[0052] Comparative Example 1 The comparative example refers to the content of Example 1, except that in S1, the particles are crushed to 20 mesh, and the rest of the content is the same as in Example 1.

[0053] Comparative Example 2 The comparative example is the same as that in Example 1, except that in S2, 1 gram of toner solution is 5 ml. The rest of the contents are the same as in Example 1.

[0054] Comparative Example 3 The comparative example refers to the content of Example 1, except that the microwave power in S4 is controlled at 210W, and the rest is the same as Example 1.

[0055] Comparative Example 4 The comparative example refers to the content of Example 1, except that the volume percentage of water vapor in the mixed gas in S4 is 21%, and the rest is the same as in Example 1.

[0056] Comparative Example 5 This comparative example is based on the content of Example 1, except that the acid concentration in S5 is 0.7 mol / L, and the rest is the same as in Example 1.

[0057] Comparative Example 6 The comparative example refers to the content of Example 1, except that the drying temperature in S7 is controlled at 120°C, and the rest is the same as Example 1.

[0058] Performance testing Sample preparation: Coal-based activated carbon samples for performance testing were prepared according to the methods described in Examples 1, 2, 3 and Comparative Examples 1 to 6, totaling nine groups of samples, which were labeled as Sample 1, Sample 2, Sample 3, and Comparative Examples 1 to 6, respectively, for use in subsequent performance tests.

[0059] Specific surface area and pore structure detection: The nitrogen adsorption-desorption method was used. Approximately 0.1 g of dried activated carbon sample was placed in the sample tube of the fully automated specific surface area and porosity analyzer and pretreated under vacuum at 150°C for 6 hours to remove adsorbed moisture and impurities from the sample surface. Subsequently, the sample tube was cooled to liquid nitrogen temperature of -196°C, and the nitrogen adsorption-desorption isotherm was measured to obtain the specific surface area and pore size distribution of the sample. Test standard: GB / T19587-2017 "Determination of specific surface area of ​​solid materials by gas adsorption BET method".

[0060] Iodine adsorption value detection: First, weigh approximately 0.5 g of activated carbon sample and place it in an iodine flask. Add 10 mL of hydrochloric acid solution, boil, and simmer for 30 seconds to remove any sulfides that may be present in the sample. Cool to room temperature. Then, add 50.0 mL of 0.1 mol / L iodine standard solution, immediately stopper the flask, and shake on a shaker for 15 minutes. Then, filter quickly, take 10.0 mL of the filtrate, and titrate with 0.1 mol / L sodium thiosulfate standard solution until the solution turns pale yellow. Add starch indicator and continue titrating until the blue color just disappears. Calculate the number of milligrams of iodine adsorbed per gram of activated carbon by the volume difference of sodium thiosulfate consumed. Test standard: GB / T12496.8-2015 "Test Methods for Iodine Adsorption Value of Wood-based Activated Carbon".

[0061] Methylene blue adsorption value detection: First, weigh approximately 0.1 g of dried activated carbon sample and place it in a stoppered conical flask. Add 50 mL of a 150 mg / L methylene blue standard solution, tighten the stopper, and place the flask in a constant temperature shaker at 25°C and a speed of 150 rpm for at least 1 hour until adsorption equilibrium is reached. Then, take an appropriate amount of solution, centrifuge it, and use a UV-Vis spectrophotometer to measure the absorbance of the supernatant at a wavelength of 665 nm. Calculate the remaining methylene blue concentration based on the standard curve to obtain the methylene blue adsorption capacity of the activated carbon. Test standard: GB / T12496.10-1999 "Test Methods for Wood-based Activated Carbon: Determination of Methylene Blue Adsorption Value".

[0062] Strength testing: First, the prepared activated carbon sample is crushed and sieved to separate particles with a diameter between 1.0 and 2.0 mm. Approximately 50 grams of sample are weighed and their mass is recorded. Then, the sample is placed in the steel cylinder of the strength testing instrument, which contains a specified number of steel balls. After tightening the cylinder lid, the cylinder is rotated at a rate of 125 revolutions per minute, causing the steel balls to impact and abrade the activated carbon particles. After rotating for a certain period of time, the sample is removed and sieved using the original sieve. The mass of particles that fail to pass through the sieve is weighed. The strength is expressed as the abrasion rate, which is the percentage of the sample's mass loss relative to the original sample mass. Test standard: Appendix A, Strength Determination Method, of GB / T30202-2013 "Coal-based Granular Activated Carbon for Desulfurization and Denitrification".

[0063] pH and ash content detection: The pH detection procedure is as follows: add 2.0 g of activated carbon sample to 50 ml of distilled water without carbon dioxide, boil for 5 minutes, cool and filter, and then measure the pH value of the filtrate with a pH meter; The ash content detection procedure is as follows: place about 1.0 g of dried activated carbon sample in a pre-weighed crucible, ignite it in a high-temperature furnace at 800℃ until constant weight, cool and weigh it, and calculate the percentage of residue after ignition relative to the original sample mass.

[0064] Test standards: pH value testing refers to GB / T12496.7-1999 "Test Methods for Determination of pH Value of Wood-based Activated Carbon"; ash content testing refers to GB / T12496.3-1999 "Test Methods for Determination of Ash Content of Wood-based Activated Carbon".

[0065] Table 1: Group Specific surface area (m² / g) Iodine adsorption value (mg / g) Methylene blue adsorption value (mg / g) strength(%) pH value Ash content (%) Example 1 1550 1200 195 96.0 5.9 3.8 Example 2 1820 1450 230 95.5 6.0 3.5 Example 3 1980 1580 250 95.0 6.2 4.2 Comparative Example 1 950 750 120 96.8 5.1 4.5 Comparative Example 2 880 700 110 91.5 5.2 7.5 Comparative Example 3 780 650 95 93.0 4.7 5.0 Comparative Example 4 720 600 90 92.5 5.4 5.5 Comparative Example 5 1350 1050 160 94.5 3.5 6.8 Comparative Example 6 1420 1100 170 88.0 5.8 4.0 Example Conclusion: Based on Examples 1-3 and Comparative Example 1, and in conjunction with Table 1, it can be seen that controlling the particle size of the pulverized coal raw material within the range of 40 to 200 mesh is beneficial for forming a more developed pore structure during the subsequent activation process. When the particle size is too large, it will reduce the specific surface area and reactivity of the raw material, resulting in a weakening of the synergistic activation effect of water vapor and catalyst, which is not conducive to the formation of high-performance activated carbon. Based on Examples 1-3 and Comparative Example 2, and in conjunction with Table 1, it can be seen that controlling the amount of iron-based catalyst added within the range of 10 ml to 30 ml of 1 gram carbon powder solution can help achieve sufficient catalytic activation and obtain a high-purity product. When the amount of catalyst added is insufficient, it is not only difficult to promote pore development, but also leads to insufficient activation reaction, resulting in an increase in residual metal impurities, which in turn affects the chemical purity and adsorption performance of the product. As can be seen from Examples 1-3 and Comparative Example 3 and Table 1, a suitable microwave power can ensure the smooth progress of the activation reaction; when the power is too low, it will not be able to provide enough energy to start and maintain the activation reaction, resulting in insufficient gasification etching of the carbon skeleton, making it difficult to form a sufficient pore structure and deteriorating the adsorption performance of activated carbon. As can be seen from Examples 1-3 and Comparative Example 4, and Table 1, water vapor concentration is the core factor in regulating the pore-forming reaction. Within the preferred water vapor concentration range of this invention, it can produce good synergy with microwave heating and catalyst to achieve controllable deep pore formation. If the water vapor concentration is too low, the pore-forming reaction kinetics are insufficient, making it difficult to effectively etch the carbon matrix, resulting in poor pore structure development and low specific surface area of ​​the product. As can be seen from Examples 1-3 and Comparative Example 5 and Table 1, using an appropriate acid concentration for post-treatment can help remove catalyst residues and protect the formed pore structure, ensuring the chemical purity of the final product. When the acid concentration is insufficient, iron impurities will not be completely removed, which will not only increase the ash content of the product, but the residual acidic substances will also affect the pH value of the product and limit its application range. As can be seen from Examples 1-3 and Comparative Example 6, and Table 1, using mild drying conditions can help maintain the integrity of the activated carbon product; at the same time, excessively high drying temperatures can cause the carbon skeleton to shrink, crack, or even collapse due to thermal stress, reducing the mechanical strength of the product and thus affecting its service life and application performance.

[0066] The above embodiments are merely explanations of this application and are not intended to limit it. Any modifications made to these embodiments by those skilled in the art after reading this specification, without contributing any inventive step, should fall within the protection scope of this application.

Claims

1. A method for preparing coal-based activated carbon through one-step microwave heating-assisted steam activation, characterized in that, Includes the following steps: S1. Raw material preparation: Low-rank coal is crushed to obtain pulverized coal raw material; S2, Addition of iron-based catalyst: The iron-based catalyst solution is mixed with the coal powder raw material obtained in S1 to form the raw material to be mixed; S3. Preparation of Mixed Materials: The raw materials to be mixed obtained in S2 are impregnated in an iron salt solution. By calculating and adjusting the optimal liquid-solid ratio, concentration, temperature, and pH value, a uniformly and fully impregnated mixture is obtained. S4. Microwave activation: The mixed powder obtained in S3 is placed in a microwave field, and a mixture of water vapor and inert protective gas is introduced at the same time to activate it and obtain the activated material. S5. Pickling: The activated material obtained in S4 is soaked in acid to remove the iron element and obtain the pickled activated carbon intermediate. S6. Washing: The acid-washed activated carbon intermediate obtained in S5 is washed with deionized water until the washing solution is neutral and no chloride ions are detected, thus obtaining the water-washed activated carbon. S7. Drying: The activated carbon obtained in S6 after washing is dried to remove moisture and obtain coal-based activated carbon.

2. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S1, the pretreatment of the coal powder raw material includes: crushing the raw coal to a particle size range of 40-200 mesh, and then oxidizing the crushed coal powder in air at 80-100°C for 3-7 days.

3. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S2, the iron-based catalyst is ferric chloride hexahydrate prepared into an aqueous solution, with the iron salt FeCl3 concentration of 0.05-0.5 mol / L and 1 gram of carbon powder solution in 10-30 ml.

4. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S3, the mixing treatment is carried out by impregnation, wherein the concentration of iron salt FeCl3 is 0.05-0.5 mol / L, 1 gram of carbon powder corresponds to 10 ml-30 ml of solution, the stirring temperature is 40℃-80℃, the pH value is 3.0-6.0, the stirring speed is 200 rpm-600 rpm, and the time is 30-120 min.

5. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S4, the microwave frequency of the microwave field is 2450MHz, the microwave power is controlled between 300-600W, and the activation time is controlled to be maintained between 30-100 minutes.

6. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S4, the volume percentage of water vapor in the mixed gas is 30%-60%, and the inert protective gas is one or more of nitrogen, helium, or argon.

7. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S5, the acid used is hydrochloric acid with a concentration of 1-2 mol / L, the soaking time is 1-5 hours, and the pickling temperature is maintained at 60-80℃.

8. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S5, the liquid-solid mass ratio of the acid solution to the activated material is controlled to be (10:1) to (16:1).

9. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S6, the washing is performed 2-4 times, with each wash using 3-5 times the mass of the activated carbon intermediate and each washing process involving stirring for 10-30 minutes; followed by soaking and washing in hot deionized water at 50-70°C for 30-60 minutes.

10. The method for preparing coal-based activated carbon by microwave heating-assisted steam activation in one step according to claim 1, characterized in that, In step S7, the drying temperature is controlled at 80-90℃ until the quality of the activated carbon remains constant.

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